Question

我有3个SQL表：调制解调器，ModemsImage和ModemsPckg

    +----+-------+----------+
    | MID| Name  | Desc     |
    +----+-------+----------+
    | 1  |RNO-505|Wifi Modem|
    +-----------------------+

    +--- -+----+---------+
    | MIID| MID| ICON    |
    +-- --+----+---------+
    | 1   |1   |Cloud.png|
    +-- --+----+---------+
    | 2   |1   |Wire.png |
    +--------------------+

    +-----+--------+------------+-----+---+
    |MPKID|PckgName|PDesc       |Price|MID|
    +-----+--------+------------+-----+---+
    |1    |basic   |Starter Pckg|20.5 |1  |
    +-----+--------+------------+-----+---+
    |2    |Enhanced|advance pckg|66.5 |1  |
    +-------------------------------------+

我想要的最终结果：

    +----+-------+----------+-----+---------+-----+--------+------------+-----+
    | MID| Name  | Desc     | MIID| ICON    |MPKID|PckgName|PDesc       |Price|
    +-----------------------+-----+---------+-----+--------+------------+-----+
    | 1  |RNO-505|Wifi Modem| 1   |Cloud.png|1    |basic   |Starter Pckg|20.5 | 
    +-----------------------+-----+---------+-----+--------+------------+-----+
    | 1  |RNO-505|Wifi Modem| 2   |Wire.png |2    |Enhanced|advance pckg|66.5 | 
    +-------------------------------------------------------------------------+

我正在使用此查询：

select * from modems a join ModemsImage b on a.mid=b.mid join ModemsPckg c on a.mid=c.mid

但是这不会给我正确的输出，它返回的重复记录只是MPKID是不同的。谢谢 编辑:: 当我使用时，此查询显示我完美的2条记录

    select c.MPKID from modems a join ModemsImage b on a.mid=b.mid join ModemsPckg c on a.mid=c.mid group by c.MPKID

但是当我试图检索更多列时，它就开始复制行。

Answer 1

调制解调器有1行，其中MID = 1。
ModemsImage有2行，其中MID = 1。
ModemsPckg有2行，MID = 1。

您正在通过MID连接它们，以便获得：

Modems 1st row + ModemsImage 1st row + ModemsPckghave 1st row
Modems 1st row + ModemsImage 1st row + ModemsPckghave 2nd row
Modems 1st row + ModemsImage 2nd row + ModemsPckghave 1st row
Modems 1st row + ModemsImage 2nd row + ModemsPckghave 2nd row

为什么你会期待别的什么？

Answer 2

您需要在ModemsImage和ModemsPckg上添加其他条件。例如：

select * from modems a 
INNER JOIN ModemsImage b on a.mid=b.mid 
INNER JOIN ModemsPckg c on a.mid=c.mid AND b.MIID=c.MPKID

SQL-连接多个表

2 个答案: